Due to the popular propagation of cellular phones, noise pollution caused by incoming call ringtone leads to introduction of a new type of silence incoming call, such as vibration. Such a new type of silence incoming call is realized by a technology of notifying a user of the incoming call or reception of a text message by applying an electromagnetic force to a weight to vibrate the weight.
The incoming call notification of the vibration type according to the related art generally employs a technology of eccentrically mounting a rotating vibrator to a motor. The above technology has drawbacks in that it does not guarantee an extended lifespan, the speed of response is not fast, and it is limited to various vibration modes. Accordingly, with the trend in rapid popularization of a smartphone of a touch type, referred to as a touch phone, it is limited to meet the demand of users.
In order to solve the above problems, a linear vibration generating device has been proposed to generate vibration by linearly oscillating a weight. The proposed linear vibration generating device is configured to generate the desired vibration by linearly oscillating the weight with interaction between an electric field caused by a coil, to which a current is applied, and a magnetic field caused by a permanent magnet enclosing the coil.
Korea Patent No. 1254211 (Published on Apr. 18, 2013, entitled “Linear Actuator”, hereinafter referred to as the related patent document) discloses a technology of generating the vibration by linearly oscillating the weight. The technology disclosed in the related patent document is to maintain stable operation characteristics by increasing magnetic efficiency and to miniaturize the device.
The linear actuator disclosed in the related patent document will now be described in detail with reference to FIG. 1.
Referring to FIG. 1, the linear actuator includes a vibrator 115, a stator 110, and cases 135 and 102 for protecting the vibrator and the stator. The vibrator 115 has a magnet 111 for producing the magnetic field and a weight 112 enclosing the magnet. The stator 110 has a yoke 107 installed at a center of the lower case 102 and a coil 106 disposed around the yoke 107.
A PCB 105 is disposed at a center of a top surface of the lower case 102 so as to be electrically connected to the coil 106 and thus transmit an electric signal to the coil from the exterior. An elastic member 120 is interposed between the upper case 135 and the weight 112, or the lower case 102 and the weight 112 to elastically support the vibrator 115 and limit an amplitude of vibration within a desired value.
In order to increase a magnetic flux density with the magnetic shield, an upper plate 113 and a lower plate 114 are provided to top and bottom surfaces of the magnet 111 to in such a way of being brought into closely contact with each other to cover the upper and lower portions of the magnet 111, and dampers 140 and 142 are attached to one surface of the upper case 135 and one surface of the lower case 102 which face the plates 113 and 114, respectively.
The dampers 140 and 142 serve as a shock absorbing member capable of preventing the top and bottom surfaces of the vibrator 115 from coming into contact with the cases 135 and 102 when the vibrator 115 oscillates in the vertical direction. The dampers serving as the shock absorbing member can reduce noise generated when the vibrator 115 comes into contact with the cases 135 and 102.
According to the above related art, when the electric signal (AC power) is input to the coil 106 through the PCB 105, the vibrator 115 vertically oscillates relative to the stator 110 by use of the interaction between the electric field generated by the stator 110 and the magnetic field generated by the magnet forming the vibrator 115.
However, the configuration disclosed in the related patent document has the following problems.
First, since the dampers are provided at inner upper and lower positions of the case, and the plates 113 and 114 having a desired thickness are provided on the top and bottom surfaces of the vibrator, it is not easy to secure a sufficient stroke distance, that is, an amplitude, so that the vibrator vibrates in the limited space of the case. As a result, the height of the case should be increased, which does not meet the miniaturization of the device. Also, the above-described related art has another problems of producing noise due to collision between the vibrator and the case, and being limited to thinning of the actuator due to the magnetic shield or the like.
Finally, in the process of generating vibrating the vibrator, since the vibrator undergoes lateral wobble, that is, pitching motion, as well as the vertical oscillation, an outer corner of the vibrator comes into directly contact with the case, which causes the noise to produce, thereby deteriorating the quality and reliability of the product.